The present invention relates to efficient calculation and informative display of electromagnetic wave effects in the design of communication systems. More particularly, the present invention supports a modeling technique which facilitates the design of wireless communication systems within buildings, wherein electromagnetic wave xe2x80x9cconesxe2x80x9d emanating from point sources cover all space without overlap, and electromagnetic effects such as signal coverage are accumulated for display on horizontal planes.
Presently, indoor wireless communication systems employ radio frequency (RF) antennas located throughout a building complex so that adequate coverage is maintained. When designing such a system for a building complex, the designer must consider signal reflection from and transmission through building structures. Electromagnetic properties of building materials related to reflection and transmission can be measured under controlled conditions and tabulated for the use of designers. Moreover, buildings can be represented as collections of rectangular boxes, with electromagnetic transmission and reflection properties represented by parameter values assigned to box sides. To apply such models to the design of communication systems, computer software is required which can comprehensively display coverage resulting from a given design. Lacking such a tool, it will be appreciated that designers err on the side of including too many antennas operating at excessively high power levels, increasing both the purchase costs and operation costs of communication systems. Even so, there is no practical way to ensure that all necessary signal coverage within a building complex has been attained.
It is known to employ ray tracing, a form of physical optics, in evaluating wireless communication systems as disclosed in U.S. Pat. Nos. 5,491,644 and 5,574,466. The design systems of these disclosures employ ray tracing as part of a validation of wireless communication transfer characteristics. Unfortunately, these systems do not support interactive design of communication systems through comprehensive displays of coverage, because they are limited in the number of receiver test points for which signal coverage can be calculated. A coverage display of sufficient resolution for interactive system design requires thousands of receiver points.
The present limitation on numbers of receiver points is inherent in the method of physical optics employed by systems of the prior art. As taught in the above disclosures, the ray tracing technique employed in these systems works backwards from a receiver point to identify sources and associated signal paths. The calculations must account for rays coming into the receiver point from all possible directions. To do this task for large numbers of receiver points is impractical.
In a communication system design, there are few source points, compared to the number of receiver points desired for display purposes. It is therefore practical to consider rays in all directions emanating from source points. Each ray is considered once, along with each of its subsidiary rays generated by reflections from building walls. Rays are processed in a forward direction from source to receiver. As transmissions and reflections occur, a tree of ray segments is generated, still relatively few in number compared to the number of receiver points. As a ray and its generated ray segments are processed, its effects on each of the receiver points of the coverage display can be accumulated.
An important feature of an interactive design environment is to respond in a timely fashion to small changes in the design. In the backward solving physical optics systems of the present art, all ray processing must be repeated in response to a change of position of any transmitter. In a forward solving system, only the changed transmitter""s signal coverage need be computed. To support this feature, it is only necessary to accumulate electromagnetic effects at the receivers separately for each transmitter, combining these effects for each display.
By reliance on backwards construction of ray paths, the present art cannot take into account the relative strength of each transmitter for efficient generation of ray segments in a building complex. Paths must continue until they exhaust the possibility of reaching the strongest transmitter.
The present art does not extend to the forward solving physical optics described above, for lack of solution to certain technical problems which are the subject of the present invention. Specifically, the present art does not teach how to approximate efficiently a spherical signal wave front by a discrete set of approximately equal cones, each representing the local effects of the wave in the neighborhood of a ray. Nor is it taught how to propagate the boundaries of such cones accurately so that discrete contributions of a source to a display point are not missed, nor covered more than once. It has therefore not been taught how to model antenna transmission characteristics within such a system, so as to compute the effects of orientation of transmitters. The present art does not teach how to determine efficiently and accurately which display points are significantly affected by a ray.
These elements, along with provisions for handling reflected as well as transmitted wave propagation within a building, together constitute a system of physical optics which is the subject of the present invention. This system, referred to in this description as the cone mapping method, permits the scientific and empirical knowledge of electromagnetic wave propagation evidenced in the current art to be applied in a timely manner to the computation of displays of signal coverage of a communication system in a building complex.
Therefore, an object of the present invention is to provide efficient computational techniques enabling signal coverage displays for the interactive design of communication systems within buildings, such design determining adequate placement, orientation and power level of transmitters of a wireless communication system.
Another object of the present invention, as set forth above, is to project signal coverage throughout areas of interest in a building complex, to a resolution required for displays ensuring adequate coverage.
A further object of the present invention, as set forth above, is to represent signal transmission from directionally oriented transmitters to large numbers of receiver test points in a discrete model, without introducing erroneous artifacts of the discrete model through computational inaccuracies.
Still another object of the present invention, as set forth in brief above, is to model each transmitter as a discrete set of rays corresponding to an antenna pattern registered with the modeling program.
Yet another object of the present invention, as set forth above, is to limit the generation of ray segments to those with sufficient strength to affect test receivers significantly.
A further object of the present invention, as set forth above, is to respond interactively to small changes in the design of the communication system being modeled, by computing and maintaining signal coverage values separately for transmitters of the design.
The foregoing and other aspects of the invention, which shall become apparent as the detailed description proceeds, are achieved by a modeling method for determining the signal coverage provided by a wireless communication system of at least one point source such as a transmitter and at least one receiver in a modeled building, comprising the steps of covering completely and without overlap, the space around a point source by a plurality of cones of appropriate size and shape, assigning relative signal strength to each of the plurality of cones based on the angular orientation of a transmitter at the point source and a spherical antenna pattern associated with the transmitter, processing in a forward direction from the point source to the receiver a center ray segment of each plurality of cones corresponding to transmitted and reflected portions of the center ray segments in uninterrupted travel between modeled building surfaces, providing receiver test points arranged in regularly spaced, rectangular, planar test point grids, computing the intersection of the cones with the receiver test point grids, and enumerating the receiver test points within the cone intersections for the accumulation of electromagnetic effect of the ray segment on the receiver test point.
Yet another aspect of the present invention is attained by a computer-readable medium for determining signal coverage of a wireless communication system within a building, comprising means for storing a model of the building features including at least walls, floors and openings, the storing means also storing transmissive and reflective properties associated with the building features, means for assigning at least one transmitter and at least one receiver to positions on the model, means for covering the space around at least one transmitter with a plurality of cones of approximately equal size, means for associating an antenna pattern with at least one transmitter and assigning a center ray segment with a relative signal strength of the antenna pattern to each of the plurality of cones, means for associating a receiver grid pattern with at least one receiver, means for processing the center ray segment generated by the transmitter through each of the plurality of cones toward the receiver including a determination of transmission and/or reflection of the center ray segment upon impinging the building features, the processing means tracking the center ray segment until strength thereof is deemed negligible, and means for computing an intersection of the plurality of cones with the receiver grid pattern to determine if the relative signal strength is adequate to reach at least one receiver.
These and other objects of the present invention, as well as the advantages thereof over existing prior art forms, which will become apparent from the description to follow, are accomplished by the improvements hereinafter described and claimed.